1. Field of the Invention
The invention relates generally to semiconductor amplifiers and non-linear resistors actively controlled according to voltages applied to them. In particular, the invention relates to sense amplifiers having negative feedback modulated according to the amplitude of the amplifier's signal.
2. Related Art
Proximity communication is an I/O technology that allows two chips in face-to-face alignment to communicate without wires as has been explained by Drost et al. in “Proximity Communication,” IEEE Journal of Solid-State Circuits, vol. 39, no. 9, September 2004, pp. 1529-1535. In the most widely used implementation, corresponding arrays of electrode plates or pads are formed in the opposing surfaces of the two chips, which are then fixed together with a dielectric layer in between to form a large number of capacitively coupled communication links between the chips. Alternatively, the transmitting and receiving elements may be inductive loops acting as antennas or complementarily arranged optical transmitters and receivers. A transmitter on one chip impresses an electrical signal on one of its pads, and a receiver on the other chip detects the signal coupled to the corresponding one of its pads. Although proximity communication promises much higher input/output (I/O) density and lower power, detecting signals over proximity communication is a challenge. Signals coupled onto the plates of the receiving chip can be very small, on the order of 10 mV. With capacitively coupled proximity communication, the receiving nodes must also be biased at appropriate DC levels.
The need to detect small signals over a capacitively coupled interface poses significant challenges to the design of data receivers. Input offset subtracts from the received signal, degrading receiving sensitivity; for robust communication, offset cancellation shall be used, especially in advanced fabrication processes where transistor mismatch effects are more significant. An additional challenge is that of biasing the receiving node at a voltage level at which the amplifier has adequate gain.